Put the verbs in brackets into the Present Perfect or Past

Put the verbs in brackets into the Present Perfect or Past Simple Tence.
1. This is the third time we (to observe) such results
2. In 1812, one of the customers at Riebau's shop, (to give) Faraday a ticket to attend the last four lectures of a course given by Humphrey Davy at the Royal Institution of Great Britain.
3. The researcher (to try) his experiments twice. He is happy with the results.
4. Vacuum cleaners, toasters, dishwashers and other appliances greatly (to improve) domestic work by reducing physical labor. Now it takes much less time and effort.
5. His laboratory (to develop) the most efficient communications networks and protocols since then.
6. Around 1600, the English philosopher and scientist Francis Bacon (to state) that heat itself is motion and nothing else.
7. The graduates of that university never (to receive) a solid technical foundation, so they have poor opportunities to work in many special areas